For radiation therapy procedures using linear accelerators, simulators, cobalt 60 machines, or the like, precise patient positioning is critical if therapy is to be a benefit. Typically, a patient is placed on a patient positioning device, such as a cradle or bed and the portion of the patient to be treated is placed in a radiation beam for an exposure of predetermined duration. The irradiation of the patient destroys cellular tissue or inhibits its growth to achieve the desired therapeutic benefits. As can be readily appreciated, the radiation beam must be accurately positioned with respect to the portion of a patient being treated both to insure the maximum therapy and to prevent undesirable damage to healthy tissue. To achieve the accuracy necessary for such procedures, a laser system has been used to provide horizontal, transverse, and sagittal lines of laser light that identify the therapy axis and define the exact isocenter of the radiation equipment for patient positioning.
Such positioning has commonly been carried out by locating an anatomical landmark on the patient or painting a target on the patient's skin to be irradiated. A light pattern, for example, a cross-hair or an "X", is provided along the path of the radiation beam and the patient's couch is moved so that the target on the skin is aligned with the lighted pattern. The lighted pattern may then be removed, the area around the patient evacuated of personnel and the radiation beam established.
In the creation of a light pattern to position the patient, laser lines are generated by an apparatus typically comprising a laser, a beam expanding telescope, and a cylindrical lens, all of which are mounted within a wall hung cabinet. In such a design there are three axes that must be aligned: (1) the laser tube axis, (2) the telescope axis, and (3) the diverging lens or turret axis. The telescope portion of the laser line generator may comprise a pair of expensive spherical lenses. The lenses must be adjusted and arranged to produce laser lines of sufficient length, brightness, acuity, and depth of field. Because of the geometry of the lens configurations for laser line generators of the prior art, the telescope is typically buried deep in the cabinet, which is inconvenient for making necessary adjustments. For lens configurations of the prior art utilizing a beam splitter (for double-line or "cross" generators) and mirrors to direct the light beam emanating from the laser, additional adjustments must be made. The lens configurations for laser line generation in accordance with the prior art are therefore usually time-consuming to adjust and often require expensive optics.